Combining Restricted Grazing and Nitrification Inhibitors to Reduce Nitrogen Leaching on New Zealand Dairy Farms

Abstract

Intensification of pastoral dairy systems often means more nitrogen (N) leaching. A number of mitigation strategies have been proposed to reduce or reverse this trend. The main strategies focus on reducing the urinary N load onto pastures or reducing the rate of nitrification once the urine has been deposited. Restricted grazing is an example of the former and the use of nitrification inhibitors an example of the latter. A relevant concern is the cost effectiveness of these strategies, independently and jointly. To address this concern, we employed a modeling approach to estimate N leaching with and without the use of these mitigation options from a typical grazing dairy farm in New Zealand. Three restricted grazing options were modeled with and without a nitrification inhibitor (dicyandiamide, DCD) and the results were compared with a baseline farm (no restricted grazing, no inhibitor). Applying DCD twice a year, closely following the cows after an autumn and winter grazing round, has the potential to reduce annualized and farm-scale N leaching by ∼12%, whereas restricted grazing had leaching reductions ranging from 23 to 32%, depending on the timing of restricted grazing. Combining the two strategies resulted in leaching reductions of 31 to 40%. The abatement cost per kilogram of N leaching reduction was NZ$50 with DCD, NZ$32 to 37 for restricted grazing, and NZ$40 to 46 when the two were combined. For the range analyzed, all treatments indicated similar cost per percentage unit of mitigated N leaching, demonstrating that restricted grazing and nitrification inhibitors can be effective when used concurrently.

The implications of winter milk premiums for sustainable profitability of dairy systems

“…While more milk production in autumn and winter generally leads to an increase in nitrogen leaching, the use of a feed pad during this critical period can reduce or minimise nitrogen leaching (Romera et al 2017). This concurs with results from Pastoral 21 experiments undertaken on DairyNZ's Scott Farm, where the use of stand-off in autumn and winter reduced N leaching by approximately 20% in one of the farmlets (Selbie et al 2017).…”

Benefits and Trade-Offs of Dairy System Changes Aimed at Reducing Nitrate Leaching

“…The substantial reduction in profit compared to the relatively small reduction in production can be explained by standing cows off pasture in the Waikato Improved system. Although this mitigation has been confirmed as highly effective for nitrate leaching [1,21,22], the trade-offs are the increase in methane emissions from manure collected in effluent ponds [11,23], and the large costs of the capital investment, depreciation, and maintenance of these facilities [24,25]. The cost of the standing cows off pasture is reflected in other working expenses and overheads and resulted in a 10 cents/kg MS higher cost of milk production (Table 4).…”

Benefits and Trade-offs of Dairy System Changes Aimed at Reducing Nitrate Leaching

“…The substantial reduction in profit compared to the relatively small reduction in production can be explained by standing cows off pasture in the Waikato Improved system. Although this mitigation has been confirmed as highly effective for N leaching [1,21,22], the trade-offs are the increase in methane emissions from manure collected in effluent ponds [23,11], and the large costs of the capital investment, depreciation and maintenance of these facilities [24,25]. The cost of the standing cows off pasture is reflected in other working expenses and overheads and resulted in a 10c/kg MS higher cost of milk production (Table 4).…”